In the machining and other manufacturing fields, a coolant, which is mostly comprised of industrial use water, has been used for various purposes, such as lubrication and cooling at the time of machining, and washing and degreasing after machining. These coolants have cutting fluid, cleaning solution, and other various components added in accordance with the purpose of use. After use, they are recovered in the state of a waste liquor in which swarf and the oil for lubrication use are mixed. The recovered waste liquor is recirculated for use after removing the foreign matter. As the apparatus for such waste liquid treatment, in the past, various types of apparatuses have been used (for example, see PLT 1).
The prior art which is shown in this PLT 1 employs the following screw pipe type of liquid separation mechanism. At the inside of a cylindrical outside member, a rod-shaped inside member which rotates relative to the outside member is coaxially arranged. A spiral-shaped guide partition, which is provided at the outer circumference of the inside member, is made to slidingly contact the inner circumferential surface of the outside member. At the time of operation, the bottom part of the screw pipe is immersed in the mixed liquid to be separated. In that state, the outside member and the inside member are made to rotate relative to each other. Due to this, the guide partition slidingly contacts the inner circumferential surface of the outside member while rotating. The oil which floats on the surface of the mixed liquid and other substances for separation are transported upward along the spiral surface of the guide partition to be separated and recovered.